The best games I had were always the ones I could hit both sides of the plate. I think just living away is a recipe for being singled to death because decent hitters will adjust and shoot it through the right side.
That being said, learning to hit the inside corner is tough. Younger kids with poor mechanics miss arm side, as we see on this site daily with kids flying open too early. Hence, getting a kid to throw inside without fear of drilling the hitter is a real task. I always found it a little easier to come inside on a lefty as a right handed pitcher. The angle was just more appearing. Even later in my career I found it difficult to commit to a pitch when my catcher was set up under the righty’s hands. That target just looks so small. As a natural sinker baller from the side, I just started telling my catcher to set up down the pipe and let it tail in there on its own.
The quote you posted is spot on though. Even a slower fastball is intimidating to a hitter when doesn’t expect it so tight to his body. It takes a really gifted hitter to honestly get his hands to an inside fastball without cheating with the lower half and opening early. That being said, I think at lower levels the outside corner is more effective because of that very point. Most batters are nervous and step in the bucket slightly - hence the power of the outside corner.